KR20130054428A - Optical measuring system for determining distances - Google Patents

Abstract

Sensor devices (designed and developed in consideration of the most reliable distance measurement, which can be measured in any kind of measurement situation, a detector that detects a light source generating an irradiated light beam and a portion of the irradiated light beam reflected from the surface of the object under test. A measurement system for determining the distance between the measured object and the object under test (designed to be transparent for at least the visible wavelength range), in which the irradiated light beam has a wavelength in the violet or ultraviolet region. The light beam is designed such that the irradiated light beam is diffusely reflected at the surface of the object under test. In addition, this measurement system is specific for measuring an object that is inherently opaque.

Description

Optical measuring system for distance determination {OPTICAL MEASURING SYSTEM FOR DETERMINING DISTANCES}

The present invention relates to a sensor device comprising a light source for generating an irradiation light beam and a detector for detecting a portion of the irradiation light beam reflected from the surface of the object and at least a distance between the object being designed to be transparent to at least the visible light wavelength range. It relates to a measurement system for determining.

The present invention also provides a method for determining a distance between a sensor device comprising a light source for generating an irradiation light beam and a detector for detecting a portion of the irradiation light beam reflected from a surface of the object and a target under test designed so that visible light is reflected directly. To a measuring system.

Optical measuring systems have a wide range of practical applications. Accurate and fast contactless measurement opens up many applications in which the distance between an object to be measured and a sensor device can be measured in a non-contact state or to be measured without damaging the object. One important application is quality assurance (QA) for inspecting the quality of workpieces.

The optical measuring system irradiates an object with an illumination light beam (a red or infrared laser beam is used very frequently) and detects a part of the irradiation light beam reflected from the object under measurement by a detector. . Various methods are known from experience depending on how such a sensor device can be used to determine what is the distance from the sensor device to the object under test. As an example, reference is made to triangulation.

Measurement systems known in the prior art are always problematic when performing measurements on a workpiece under transparent or partially transparent conditions. Transparent in this context means that a wide range of spectral regions of visible light (wavelength range 400 nm to 800 nm) can pass through the object under test. During the pass, the spectral region is only slightly attenuated. Partially transparent means that at least one spectral region of visible light can pass through the object under test and the other spectral region is completely or negligibly absorbed or reflected.

When the irradiated light beam hits this type of object under test, it is reflected directly. That is, the incident angle of the irradiation light beam on the surface of the object to be measured is equal to the reflection angle of the reflected irradiation light beam. There is virtually no dispersion in the spatial direction. For this reason, the sensor device and the object to be measured must be optimally aligned to obtain useful measurement results. Even if the surface of the object to be tilted only slightly at the optimum position, the irradiated light beam does not reflect to the detector, so the measurement procedure fails and becomes quite unstable. Especially during quality assurance in a manufacturing environment, it is virtually impossible to maintain optimal alignment between the sensor device and the object under test. This alignment is practically impossible with curved or rounded workpieces. Similar problems arise in optical measurements on opaque objects that do not reflect light directly due to surface finish. These problems are comparable here to each other. As an example, a mirror surface is referred to.

Thus, the present invention provides a measurement system of the form named at the outset for a transparent, partially transparent, or opaque measurement object that can reliably perform optical distance measurements even on an object on the surface where direct reflection occurs. The objective is to design and develop a framework.

According to the invention, this object for transparent and translucent objects is achieved by the features of claim 1. Accordingly, in the measurement system to be discussed below, the irradiated light beam has a wavelength in the violet or ultraviolet region, and the object to be measured is designed such that the irradiated light beam is diffusely reflected at the surface of the object. ,

In measuring on an opaque to-be-measured object, this object is achieved by the features of claim 5. According to this, in the measurement system to be discussed below, the irradiated light beam has a wavelength in the violet or ultraviolet region, and the object to be measured is designed such that a coating is formed on the surface to diffusely reflect the irradiated light beam.

In the manner according to the invention, it should be recognized first of all that the transparent or translucent subject matter is very frequently designed to be opaque or to have a high degree of light attenuation for light in the violet or ultraviolet wavelength range. Usually this feature is intentionally implemented as a protective measure. In particular, plastics tend to lose their transparency when exposed to ultraviolet light for a very long time. In order to prevent this effect, plastics are treated such that purple and / or ultraviolet light is hardly or rarely transmitted into the material. Rather, purple and / or ultraviolet light is diffusely reflected at the surface of the material. The opacity or large degree of light attenuation of such an object is used in the measurement system according to the present invention.

According to the present invention, the light beam of the violet or ultraviolet wavelength band is used as the irradiation light beam. The irradiation light beam that is diffusedly reflected without being directly reflected can be obtained in an unexpectedly simple manner by combining the object to be measured and the irradiation light beam. For this reason, even a transparent or translucent measurement object can be measured using an optical measurement system without affecting the optical properties of the measurement object in the visible light region.

According to the present invention, this characteristic combination can be used for an opaque object to be measured, that is, a material which does not transmit visible light in fact and whose visible light is directly reflected from the surface thereof. To this end, in the present invention, a coating is formed on the object to be opaque to purple and / or ultraviolet light or to attenuate the purple or ultraviolet light to a degree that cannot be ignored. This causes diffuse reflection of the purple or ultraviolet radiation beam on the surface of the object under test.

By diffuse reflection of the irradiated light beam on the surface of the measurement object (either transparent, translucent, or opaque), the irradiated light beam is not reflected in only one spatial direction but reflected in a predetermined angle range around the direct reflected light beam do. This no longer necessitates precise alignment of the workpiece and the sensor device with each other and it becomes clear that the field of use of the measurement system is expanded. Clearly, a more stable measurement environment can be achieved.

It is preferable that the surface of the measured object on which the irradiation light beam is reflected is an outer surface facing the sensor device of the measured object. In principle, in the case of a transparent EUT, the irradiation light beam first penetrates the EUT and then either reflects off the surface facing away from the sensor device or on any separation plane located within the EUT and directed toward the detector. You can also think about it. Preferably, however, it is preferable to use a measurement object that transmits only a small amount even if the irradiated light beam does not or does not transmit.

In the case of a transparent or translucent object, the diffuse reflection of the irradiated light beam may occur in a special coating on the surface of the object. Suitable coatings for this are empirically known coatings which are opaque or high in light attenuation in the violet and / or ultraviolet region. As an example (but not by way of limitation), reference is made to coated plastic-glass.

However, it is also conceivable that the object under test already has the necessary properties due to its material composition, and that purple and / or ultraviolet light cannot significantly transmit the object under test. Those materials which are transparent to visible light and opaque in the violet and / or ultraviolet region are known from experience.

In a preferred exemplary embodiment of the measurement system according to the invention, the object to be measured comprises transparent plastic parts or coated glass for use in the automotive industry. As a particularly preferred method, the present measurement system is used when measuring a lens or a disc such as a headlight or a taillight of a vehicle.

Preferred exemplary embodiments in the case of opaque objects are related to opaque plastics, polished metal plates or various designed metal objects and the like. However, wood, wood materials, paper and the like can also be used as the opaque object. The object to be measured does not need to be completely opaque. In principle, the object to be measured may be translucent.

Preferably, the object under test (whether transparent, translucent, or opaque) is designed to be opaque or largely attenuated for light with a wavelength less than 420 nm. Particularly preferably, it is designed to be opaque or large in attenuation for light having a wavelength of 390 nm or less.

For a particularly good optical operation of the sensor device, the light source can consist of a laser which emits a laser beam as an irradiation light beam. In this case, not only a solid state laser or a gas laser but also a laser diode can be used. However, especially for cost-effective measurement systems, the light source can be constructed with LEDs. In many applications, low light quality is sufficient.

The irradiation light beam preferably has a wavelength of 425 nm or less. As a particularly preferable method, an irradiation light beam having a wavelength of 405 nm or less is used. As a very particularly preferable manner, the wavelength of the irradiation light beam is 390 nm or less. Generally, UV light of extremely short wavelength can be used as a light source. However, this type of light source is very expensive and requires special protective measures, which complicates the safe operation of the measuring system. Therefore, the limit in wavelength is decided. At present, the minimum wavelength that is technically acceptable for use is 300 nm.

The irradiation light beam is preferably irradiated to the object under test in a point shape or linearly. You can also combine points or lines to form patterns such as crosshairs or several parallel lines. It is preferable that a radiation line is a straight line.

In the beam path of the irradiation light beam, a focusing apparatus is provided after the light source to focus the irradiation light beam. The light source and the focusing apparatus together constitute an irradiation unit. The irradiation light beam is preferably focused (focusing) on the surface of the object under test. However, it is also conceivable that the irradiation light beam is focused at an infinite point or another position on the optical axis.

As a detector, a complementary metal oxide silicon (CMOS) array (array) or a charge coupled device (CCD) array can be used. This arrangement is preferably a linear arrangement or a face array (ie two-dimensional development). For example, the linear arrangement may be used when measuring distances in a point shape, and the surface arrangement may be used when measuring distances according to a grid intersection method. In some cases, the detector can also be configured with an existing line scan or matrix camera.

In the case of point-shaped distance measurement, PSD (position detection diode) or APD (avalanche photodiode) can be used. In particular, the APD can be used for distance measurement using a running time or phase shift measurement of light. PSD or APD can be mounted as an array.

A wavelength selection element may be provided in front of the detector to block radiation in areas other than the detection channel (ie, the beam path in the sensor device, of the portion of the irradiation light beam reflected off the surface of the object to be measured). By means of the wavelength selection element it is possible to block the ambient light, for example for a detector with broadband detection characteristics. This wavelength selection element can be designed as a filter (for example, an interference filter) or a dispersive element. However, for example, to reduce the size of the sensor device, the wavelength selective element may be designed as a dichroic mirror for beam deflection / folding. In general, it makes sense to match the entire optical channel (ie, the path of the irradiated light beam from the light source to the detector) to the wavelength of the irradiated light.

It is also conceivable to combine several wavelength selection elements to further improve wavelength selectivity. For example, several dispersive elements can be placed consecutively. However, it is desirable to combine various kinds of wavelength selective elements with each other. This means that it is possible to combine a chromatic mirror with a filter or a dispersion element.

The measurement system preferably includes an evaluation unit connected to the sensor device and receiving a measurement signal of the sensor device. This evaluation apparatus can receive additional information about the irradiation light beam, for example, when the irradiation light beam is modulated. The evaluation device uses the received light beam (i.e. the part of the irradiation light beam reflected and received by the detector) and, if possible, using known information about the irradiation light beam itself, the sensor device and the object to be measured. Determine the distance between. The distance can be determined, for example, by reading a value from a table having contents determined by calculation or at the time of calibration measurement and stored in the evaluation unit.

In addition to or as an alternative to the information about the irradiated light beam, the evaluation unit may receive information about the intensity of the light reflected from the object under test, and using a control device according to the intensity of the light source, the detector and / or the detector It is possible to adjust and / or adjust the integration time of the signal amplifier installed in the line.

The sensor device and the evaluation unit can be designed to measure distance by triangulation. To this end, the light source and the detector are arranged so that the light source, the irradiation point shining on the surface of the object to be measured, and the irradiation point shining on the detector form a triangle. Since the sensor device is known, the distance of the point irradiated on the surface of the object to be measured can be calculated by the sensor device.

The sensor device and the evaluation unit can also be designed to determine the distance by measuring the travel time of the light. To do this, it is measured how long it takes for the light beam to travel from the light source to the workpiece and to the detector. Since the speed of light is known, the distance can be determined from this time.

Another possible design of the sensor device and the evaluation unit involves the measurement of phase shift. To do this, the brightness of the irradiated light beam is modulated with respect to an appropriate frequency, and the changes in the brightness of the irradiated light beam and the received light beam are compared with each other. From the mutual phase position, it is possible to determine the travel time of the light and consequently the distance between the sensor device and the object under test.

The evaluation unit may combine several distance measurements such that the contour (profile) of the object and / or part of the object is shown. To do this, it relates to the measuring point position and distance values on the workpiece. If the sensor device is operated according to, for example, a grid crossing scheme, it is possible to determine the contour of the line in one measurement. Passing this line on the object under test allows the three-dimensional structure of the object or part of the object to be determined. For contour determination, the sensor device and the object under test can also be designed to move with each other. However, it is also possible to use a deflecting device to move the irradiated light beam over the object under test. Suitable scanning devices for this are known empirically.

According to a particularly preferred exemplary embodiment, the present invention relates to a measurement system according to triangulation, which is used to measure the distance to an object that partially absorbs and partially reflects UV light because of the coating or its material composition. will be. A light irradiation apparatus (eg, a laser diode with focusing optics) emits focused light having an emission wavelength in the UV band. On the receive beam path, the selection of this wavelength among several wavelengths can be done using a dichroic mirror equipped with an optical filter, a dispersive element, and / or a suitable shading plate. Some of the light emitted is diffusely reflected at the surface of the object and / or from the object in the receive beam path.

There are now various possibilities for designing and further developing the idea of the invention in an advantageous manner. For this purpose, reference is made to the dependent claims of claims 1 and 5 on the one hand, and on the other hand, the following preferred exemplary embodiments described with reference to the drawings. In connection with the description of the preferred exemplary embodiment of the present invention described with reference to the drawings, the overall preferred design and development of the inventive idea will be described.

According to the present invention, there is provided a measurement system for a transparent, partially transparent, or opaque to-be-measured object, which can reliably perform optical distance measurement even on an object on a surface where direct reflection occurs.

1 shows the intensity distribution in a detector using a red irradiation light beam having a wavelength of 670 nm.
2 shows the intensity distribution in a detector using a violet irradiated light beam of 405 nm wavelength in the measurement system according to the invention.

1 and 2, both figures are calculated with the same measuring equipment. Together with the lens, the laser generates a focused laser beam that is deflected toward the vehicle headlight glass (object under test) made of plastic-glass about 2 mm thick. The laser beam is reflected at least partially from the surface of the object under test and passes through another lens, a wavelength selective filter adapted to the wavelength of the irradiated light beam, and a light shield plate of the linear detector. The sensor device performs the measurement according to the triangulation method. A surface that is opaque to ultraviolet light is formed on the surface facing the sensor device of the object under test.

Fig. 1 shows the intensity distribution when using a red laser with an emission wavelength of 670 nm in the prior art. On the one hand, there is a need for optimal alignment between the object under test and the sensor device. On the other hand, there are two distinct main peaks in the intensity distribution. In FIG. 1, the left peak is due to the irradiation light beam reflected from the surface facing the sensor device of the object under test, and the right peak is the surface at which the irradiation light beam passes through the object and is facing the sensor device of the object under test. Due to reflections from This makes the measurement unclear. Another problem is that the right peak is higher than the left peak. If you simply evaluate the intensity curve using the highest peak, you will get errors in the results of the distance calculations. If the highest peak is used to adjust the intensity and irradiation time of the irradiated light beam, the measurement may become unstable. If the object is tilted, the intensity of the first peak will be lowered and will no longer be evaluated by the sensor device, which may result in a measurement error on the reflection point on the back or inside of the object under test. The small peaks seen in the intensity distribution of FIG. 1 are due to multiple reflections occurring in the object under test.

2 shows the use of a purple laser irradiation light beam of 405 nm wavelength in accordance with the present invention. Because of the diffuse reflections on the surface of the object under test, the sensor device and the object under test can be placed more freely. In addition, in the intensity distribution according to FIG. 2, only one peak is individually displayed. Further visible small peaks indicate that a small portion of the irradiated light beam is reflected from the surface facing the sensor device through the object under test. However, the intensity of this additional peak is not important because it is low. Multiple reflections do not occur.

Further useful designs of the device according to the invention are referred to the entire part of the description and the appended claims in order to avoid repetition.

Finally, it should be clearly noted that the above-described exemplary embodiments of the apparatus according to the present invention are merely for explaining the spirit of the claims, and the spirit of the present invention is not limited by the exemplary embodiments.

Claims (18)

A sensor device comprising a light source for generating an irradiated light beam and a detector for detecting a portion of the irradiated light beam reflected from the surface of the object to be measured, and for determining a distance between an object being designed to be transparent for at least the visible light wavelength range. In the measurement system,
Wherein the irradiated light beam has a wavelength in the violet or ultraviolet region, and the object under test is designed such that the irradiated light beam is diffusely reflected at the surface of the object under test, for determining the distance between the sensor device and the object under test. Measuring system. The sensor device as claimed in claim 1, wherein one surface of the object to be measured has a coating which causes diffuse reflection of the irradiation light beam and is opaque or at least highly attenuated in the violet and / or ultraviolet wavelength band. Measurement system for determining the distance between workpieces. The distance between the sensor device and the object to be measured according to claim 1 or 2, characterized in that the object under test is designed of a material which is opaque or at least highly attenuated in the violet and / or ultraviolet wavelength band. Measuring system. The sensor device according to any one of claims 1 to 3, wherein the object to be measured is designed as a transparent plastic, or preferably as a lens or a disk such as a vehicle headlight or a vehicle tail light. Measurement system for determining the distance of the. A sensor device comprising a light source for generating an irradiation light beam and a detector for detecting a portion of the irradiation light beam reflected from the surface of the object, and a measurement system for determining a distance between the object under test and to which visible light is directly reflected. In
The irradiation light beam has a wavelength in the violet or ultraviolet region, and a coating for diffusing and reflecting the irradiation light beam on the surface of the object to be measured is formed between the sensor device and the object to be measured. Measurement system for determining the distance of, The measurement system of claim 5, wherein the object to be measured is designed from opaque plastic, metal, wood, and / or paper. 7. The measurement system of claim 1, wherein the light source consists of a laser that emits a laser beam as an irradiated light beam. 8. 8. The distance between the sensor device and the object to be measured according to claim 1, wherein the irradiated light beam has a wavelength of 425 nm or less, preferably 405 nm or less, particularly preferably 390 nm or less. Measurement system for determining the number of times. The sensor device according to claim 1, wherein the irradiated light beam is irradiated to the object under measurement in the form of dots, cross hairs, and / or several parallel lines. Measurement system for determining the distance of the. 10. A measurement system for determining the distance between a sensor device and an object to be measured according to any one of claims 1 to 9, characterized in that a light focusing device for focusing the irradiation light beam is arranged after the light source. The sensor device and the object to be measured according to claim 1, wherein the detector comprises a CMOS or CCD arrangement, preferably the arrangement is designed in a linear arrangement or a plane arrangement. Measurement system for determining the distance between. 11. The method of claim 1, wherein the detector comprises a position sensing diode (PSD) and / or an avalanche photodiode (APD). 12. Measuring system. 13. A wavelength selection element according to any one of the preceding claims, wherein a wavelength selection element is arranged in front of the detector in order to block regions other than radiation, which preferably uses a filter, a dispersion element, or a coloring mirror. A measurement system for determining the distance between the sensor device and the object under test. 14. A measurement system for determining the distance between a sensor device and an object to be measured according to claim 13, characterized in that it combines a plurality of wavelength selection elements, preferably different types of wavelength selection elements. The method according to any one of claims 1 to 14, wherein the evaluation unit is connected to the sensor device, wherein the evaluation unit measures distance using a portion of the irradiation light (received light beam) received from the detector by being reflected from the object under test. Determining a value, characterized in that for determining the distance between the sensor device and the object under test. 16. A measurement system for determining a distance between a sensor device and an object to be measured according to claim 15, wherein the evaluation unit and the sensor device are designed to perform distance measurement according to a triangulation method. The sensor device according to claim 15, wherein the evaluation unit and the sensor device are designed in such a manner as to measure the travel time of the irradiated light and the received light, or to measure the phase shift between the modulated irradiated light beam and the received light beam. Measuring system for determining the distance between the object and the object under test. 18. The method of any one of claims 15 to 17, wherein the object under test and the sensor device can be moved relative to each other, and the evaluation unit is configured to determine the contour of the object or part of the object through multiple distance measurements. A measurement system for determining the distance between the sensor device and the object under test.

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